[grid] Removing default value for max-sessions

It is already in the code then the option is retrieved,
but additionally it means that it was taking precedence
over the value configured on the `config.toml`.

This fixes SeleniumHQ/docker-selenium#1128

Author: diemol

java/server/src/org/openqa/selenium/grid/node/config/NodeOptions.java

@@ -78,9 +78,7 @@ public Node getNode() {
   public Map<Capabilities, Collection<SessionFactory>> getSessionFactories(
     /* Danger! Java stereotype ahead! */ Function<WebDriverInfo, Collection<SessionFactory>> factoryFactory) {
 
-    int maxSessions = Math.min(
-      config.getInt("node", "max-concurrent-sessions").orElse(Runtime.getRuntime().availableProcessors()),
-      Runtime.getRuntime().availableProcessors());
+    int maxSessions = getMaxSessions();
 
     Map<WebDriverInfo, Collection<SessionFactory>> allDrivers = discoverDrivers(maxSessions, factoryFactory);
 
@@ -93,6 +91,13 @@ public Map<Capabilities, Collection<SessionFactory>> getSessionFactories(
     return sessionFactories.build().asMap();
   }
 
+  public int getMaxSessions() {
+    return Math.min(
+      config.getInt("node", "max-concurrent-sessions")
+        .orElse(Runtime.getRuntime().availableProcessors()),
+      Runtime.getRuntime().availableProcessors());
+  }
+
   private void addDriverFactoriesFromConfig(ImmutableMultimap.Builder<Capabilities, SessionFactory> sessionFactories) {
     config.getAll("node", "driver-factories").ifPresent(allConfigs -> {
       if (allConfigs.size() % 2 != 0) {

java/server/src/org/openqa/selenium/grid/node/httpd/NodeFlags.java

@@ -38,7 +38,7 @@ public class NodeFlags implements HasRoles {
     names = "--max-sessions",
     description = "Maximum number of concurrent sessions.")
   @ConfigValue(section = "node", name = "max-concurrent-sessions", example = "8")
-  public int maxSessions = Runtime.getRuntime().availableProcessors();
+  public int maxSessions;
 
   @Parameter(
       names = {"--detect-drivers"}, arity = 1,